Railway track circuit apparatus



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yAZeguZazz'on begins. Tube i' H ATTORNEY Patented Nov. 5, 1940 UNETED STATES PATENT OFFIQE RAILWAY TRACK CIRCUIT APPARATUS Application September 26, 1939, Serial No.- 296,599

3 Claims.

My invention relates to railway track circuit apparatus, and particularly to apparatus for track circuits using alternating current.

In railway signaling it is well known that the voltage between the track rails adjacent the relay end of a track circuit varies with changes in ballast resistance caused by wet and dry weather conditions. Also, the current source of a track circuit when adjusted to create across the track rails under wet ballast conditions, a voltage sufficient to produce the necessary energization of the track relay, creates a higher voltage under dry ballast conditions and the relay may be overenergized. Since it is desirable to maintain a substantially uniform value of the voltage applied to a track relay regardless of variations of ballast conditions, many schemes to accomplish such results have been proposed.

Accordingly, a feature of my invention is the provision ofnovel and improved means wherewith a substantially uniform value for the voltage applied to a track relay is maintained independent of the variations of ballast resistance caused by wet and dry weather, and other maintenance conditions. Other features and advantages of my invention will appear as the specification progresses.

I shall describe one form of apparatus embodying my invention, and shall then point out the novel features thereof in claims.

In the accompanying drawing, Fig. 1 is a diagrammatic View showing one form of apparatus embodying my invention, and Figs. 2, 3, 4 and 5 are diagrams illustrating operating characteristics of the apparatus of Fig. 1.

Referring to Fig. l, the reference characters la and lb designate the track rails of a stretch of railway and which rails are formed by the usual insulated rail joints 2 into a track section AB. The track section AB is provided with a track circuit including a source of alternating current connected across the rails at one end of the section and a track relayreceiving energy from the rails adjacent the other end of the section. The source of alternating current is preferably a track transformer T4, the secondary winding 5 of which is connected across the rails la and lb adjacent the end B of section AB, over wires 6 and l, with the usual current limiting impedance 8 interposed in wire 6. The primary winding 9 of track transformer T4 is connected with any convenient source of alternating current such as a generator (not shown) whose terminals are indicated at BX and CK.

As here shown, a track relay TR of the direct current tractive armature type is controlled by the alternating current supplied to the rails through track transformer T5, track relay TR receiving energy from the track rails through a relay transformer T3 and a full-wave rectifier l l. A primary winding l2 of relay transformer T3 is connected across the rails la and lb adjacent end A of track section AB over wires l3 and It with a current limiting impedance l5 preferably interposed in wire l4. A secondary winding I5 of transformer T3 is connected across the input terminals of rectifier II, the output terminals of which rectifier are connected with winding lb of track relay TR.

In accordance with usual and well known practice, trackrelay TR is so constructed and adjusted as to operate a contact member IT at preselected pick-up and release values of energization. That is to say, when a voltage of a preselected value is applied across the terminals of the operating winding ll] of relay TR the energization effected for the relay is just sumcient to pick up and cause contact member I! to engagea front contact It to complete a circuit connection therethrough, and when the voltage applied to the operating winding ll) falls below a'preselected value the contact member l? is released to disengage front contact l8 and open the circuit connection therethrough. As is well known, such pick-up and release characteristics of a track relay are selected so as to. assure reliable response of the relay to trains entering and vacatingthe track section, and that the most satisfactory operation of the track relay is obtained for the different train speeds, train weights and other operating conditions when the voltage applied to the track relay is uniformly maintained at the preselected value notwithstanding the voltage created across the rails adjacent the track relay may vary over relatively wide limits due to variations in the ballast resistance as caused by wet and dry weather and other maintenance conditions.

According to my invention I provide a voltage regulator which limits the voltage applied to the track relay TR. Such regulator may take different forms and preferably is of the type that possesses a nearly constant voltage drop over a relatively wide range of current values such as possessed by a glow-discharge tube. In Fig. 1 such regulator'includes two electron tubes Nl and N2 connected with a secondary winding 23 of relay transformer T3. The tubes N l and N2 may be anyone of several different types and preferably are of the cold cathode gas-filled type.

Tubes NI and N2 are each provided with two electrodes, tube NI having an anode 20 and a cathode I9, and tube N2 having an anode 22 and a cathode 2|.

Tubes NI and N2 are of a construction such that current is passed more readily in one direction through the tubes than in the other. That is to say, each of tubes NI and N2 is constructed to have a forward direction and a reverse direction, current being passed in the forward direction with little impedance once the tube is rendered conductive, and current being substantially blocked in the reverse direction for all voltages Within the operating limits of the tube. Preferably, the tubes NI and N2 are alike in characteristic and are constructed to have the same starting voltage. As illustrated in Fig. 5, tube NI or N2 passes substantially no current in the forward direction of the tube until a preselected voltage (starting voltage) is applied across the tube, and once the tube is made conductive the current flowing through the tube is limited only by the impedance of other elements of the circuit in which the tube is interposed. As stated above, in the reverse direction the tube passes substantially no current within the operating limits of the tube. Tubes NI and N2 are connected across secondary winding 23 of transformer T3 in parallel and are reversed to each other as will be readily understood by an inspection of Fig. 1.

The parts are so proportioned, particularly with respect to track transformer T4 that the alternating voltage applied across the track rails at end B of track section A-B is of such magnitude that under low ballast resistance as caused by wet weather conditions, an alternating voltage is created across the rails at the other end A of the track section, which is just sufficient to cause the preselected voltage to be applied to the operating winding ID of track relay TR and relay TR is effectively energized to operate its contact member II. This alternating voltage created across the rails adjacent the track relay is illustrated by the sine curve of Fig. 2 and has a corresponding maximum or peak value of voltage. The turn ratio of secondary winding 23 of transformer T3 is such that the voltage impressed on the electrodes of tubes NI and N 2 due to the maximum or peak value of this rail-to-rail voltage which is just sufiicient to effectively operate track relay 'IR, falls just short of beingthe starting voltage of the tubes. Consequently, under such. low resistance or wet ballast conditions the tubes NI and N2 are inactive and take substantially no power away from track relay TR.

Assuming now that dry ballast conditions exist, the alternating voltage created across the rails at the end B of the track section remains the same but the voltage created across the rails at end A is materially higher than the voltage existing under wet ballast conditions. The voltage created across the rails at end A under dry ballast conditions is illustrated by the sine curve of Fig. 3. When the magnitude of the voltage during a positive half-cycle reaches the value indicated at X in Fig. 3, the voltage impressed across the electrodes of tubes NI and N2 by secondary winding 23 is equal to the starting voltage of the tubes and a particular one of the tubes, say, for example, tube NI, becomes conductive with the result that the portion of the positive half-cycle shown by dash lines in Fig. 3 is by-passed by the tube, the tube being characterized by a substantially 75 constant voltage drop over the range of voltage represented by the dash lines. It will be understood, of course, that the impedance of secondary winding 23 serves to limit the current passed by the tube NI. The voltage value at point X of Fig. 3 is only slightly greater than the maximum or peak value of the voltage curve of Fig. 2. Consequently, during the positive half-cycle the magnitude of the voltage impressed across the terminals of winding Ill of relay TR under dry ballast conditions is substantially the same as that impressed across the winding Ill under wet'ballast conditions because tube NI serves to shunt the higher values of the positive half-cycle of the railto-rail voltage. When the instantaneous value of the voltage of a positive half-cycle falls to a value slightly less than that indicated at point X, the voltage impressed across the electrodes of tube NI falls to a value less than the extinction voltage of the tube and tube NI becomes non-conductive. Hence tube NI serves to shunt the higher value of each positive half-cycle of the alternating current.

The action during the negative half-cycle of the alternating voltage is the same except tube N2, which is reversed to tube NI, serves to shunt the higher value of the voltage and limit the voltage applied to the winding 10 of track relay TR. As illustrated by the curve of Fig. 4, it is clear that the regulator including tubes NI and N2 serves to maintain a substantially uniform voltage applied to the track relay over a relatively wide range of rail-to-rail voltages.

It is to be noted that the track relay TR may be an alternating current relay connected directly to the secondary winding I6 of transformer T3- if desired. Also, it is to be noted that the relay transformer T3 may be of the autotransformer type if desired.

Although I have herein shown and described only one form of railway track circuit apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In combination, a track section, a source of alternating current connected across the rails at one end of the section to establish across the rails at the other end of the section an alternating voltage having a predetermined maximum value when low resistance ballast conditions prevail, a track relay having a preselected pick-up voltage, circuit means to connect said relay across the rails at said other end of the section to supply said relay with said pick-up voltage in response to said alternating voltage having said predetermined maximum value, twoelectron tubes of the gas-filled type each having an anode and a cathode and proportioned for the same starting voltage, and circuit means including a transformer to connect the anode and cathode of each of said tubes across the rails at said other end of the section, said transformer proportioned for applying to the tubes said starting voltage when the voltage across the rails slightly exceeds said predetermined maximum value, and said tubes disposed reversed to each other to pass the portions of both half-cycles oi the alternating voltage established across the rails above said predetermined maximum value when high resistance ballast conditions prevail.

2. In combination, a track section, a source of alternating current connected across the rails at one end of the section to establish across the rails at the other end of the section an alternating voltage having a predetermined peak value when low resistance ballast conditions prevail, a track relay having a predetermined pick-up voltage, a transformer having a primary winding connected across the rails at said other end of the section, means to connect said relay with a secondary winding of said transformer and which secondary winding is proportioned to apply to the relay said pick-up voltage when the alternating voltage across the rails is that having said predetermined peak value, two gas-filled electron tubes proportioned with like starting voltages, and said tubes connected across another secondary winding of said transformer which other secondary winding is proportioned to apply to said tubes said starting voltage when the voltage across the rails slightly exceeds said peak value, and said tubes disposed for one to pass current of one polarity and the other to pass current of the opposite polarity whereby voltages in excess of said peak value when established across the rails at said other end of the section under high resistance ballast conditions are shunted and said predetermined pick-up voltage is uniformly applied to said relay.

3. In combination, a track section, a source of alternating current connected across the rails at one end of the section to establish across the rails at .the other end of the section an alterhating voltage having a predetermined peak value when low resistance ballast conditions prevail, a transformer having a first winding connected across the rails at said other end of the section, a track relay proportioned for a preselected working energization connected with a second winding of said transformer over a rectifier for supplying to said relay a voltage sufficient to create said working energization when such low resistance ballast conditions prevail, a pair of electron tubes of the glow-discharge type with both tubes proportioned for the same starting voltage, and said tubes connected across a third winding of said transformer for supplying to said tubes said starting voltage when the alternating voltage across the rails at said other end of the section exceeds said predetermined peak value, and said tubes disposed reversed to each other to shunt the portions of both half-cycles of the alternating voltage above said predetermined peak value When high resistance ballast conditions prevail for maintaining the working energization of said relay substantially uniform regardless of ballast resistance.

WILLARD P. PLACE. 

